[PATCH RFC 08/10] xfs: Introduce xfs_fs_destroy_super()

[Kirill Tkhai <ktkhai@virtuozzo.com>]

xfs_fs_nr_cached_objects() touches sb->s_fs_info,
and this patch makes it to be destructed later.

After this patch xfs_fs_nr_cached_objects() is safe
for splitting unregister_shrinker(): mp->m_perag_tree
is stable till destroy_super_work(), while iteration
over it is already RCU-protected by internal XFS
business.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 fs/xfs/xfs_super.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 9e2ce4cd98e1..c1e00dd06893 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1774,11 +1774,20 @@ xfs_fs_put_super(
 	xfs_destroy_mount_workqueues(mp);
 	xfs_close_devices(mp);
 
-	sb->s_fs_info = NULL;
 	xfs_free_fsname(mp);
-	kfree(mp);
 }
 
+STATIC void
+xfs_fs_destroy_super(
+	struct super_block	*sb)
+{
+	if (sb->s_fs_info) {
+		kfree(sb->s_fs_info);
+		sb->s_fs_info = NULL;
+	}
+}
+
+
 STATIC struct dentry *
 xfs_fs_mount(
 	struct file_system_type	*fs_type,
@@ -1816,6 +1825,7 @@ static const struct super_operations xfs_super_operations = {
 	.dirty_inode		= xfs_fs_dirty_inode,
 	.drop_inode		= xfs_fs_drop_inode,
 	.put_super		= xfs_fs_put_super,
+	.destroy_super		= xfs_fs_destroy_super,
 	.sync_fs		= xfs_fs_sync_fs,
 	.freeze_fs		= xfs_fs_freeze,
 	.unfreeze_fs		= xfs_fs_unfreeze,